Teaching how to float

Question
Hi, I'm teaching a couple kids how to swim. I swam competivitly for 10years. I have taught my own kids to swim. I feel like I do know how to teach these kids. The problems I'm having is the two
I'm helping now are 8 & 11, they never have been around water much at all. Hench, why I want to teack them to swim.

The oldest a boy, is doing okay, he dead man floats fine, and can roll over on his back.
But I'm having trouble keeping him to keep his legs up while floating on his back. His upper body floats but legs always sink. Any tips?

The girl is doing okay, when she is relaxed she floats fine.

Both have problems with water in the face but they do put their head underwater.so we do alot of diving for rings at the bottom of the pool which helps. They both want to learn to swim very bad, so that helps them face their fears of the water.  

Answer
Sandy-
It sounds like you are doing the right things.  Don't worry about sinking legs, if he is a thin child he's not going to have much body fat to help that lower half float, and it's not really necessary to float to swim and being able to do a dead mans float is enough for safety.  As for the underwater thing, what you're doing is wonderful.  
Safety in the water is  one of the best things you can do for a child.
Good luck,
George